Image guidance of cancer ablation procedures of the liver and other organs would ideally utilize a modality capable of visualizing normal anatomic structures, the ablation electrode, the cancerous lesion, and the growing thermal lesion. When, as frequently occurs, ultrasonic methods prove inadequate in viewing the tumor, CT with and without fluoroscopic imaging, and, in very few institutions, MRI are often used to guide placement of the ablation electrode. None of these methods are both practical and successful in accurately displaying the ablated tissue during the ablation procedure with the result that, currently, liver ablations are performed in a largely "blinded" fashion. MR or CT imaging, especially during the catheter placement attempts, increases the length and cost of ablation procedures and limits the number of sites than can be practically ablated. However, MR, CT, and PET imaging remain the gold standard for assessment of ablation outcomes and imaging of potential tumor regrowth. We have developed a novel ultrasonic imaging method, Acoustic Radiation Force Impulse (ARFI) imaging, which shows great promise in real-time visualization of growing ablation lesions and, we hypothesize, will allow improved imaging of cancerous lesions in the liver. Significant challenges remain in developing ARFI imaging as an ablation guidance method and in optimizing and assessing its clinical relevance.